In a typical radio communications system, linear power amplifiers are used to broadcast communication signals from a base station. A problem in the design of a linear power amplifier is accommodating widely fluctuating input signal power levels while producing an accurate reproduction of the input signal at the output of the amplifier. The peak signal power may exceed the average signal power at any time by several decibels and even 10 decibels or more. The peak-to-average power ratio is the ratio of the peak power of a signal to the average signal power. In a linear power amplifier, the peak-to-average power ratio is a critical factor in the cost, complexity, and size of a linear power amplifier. Even a small reduction in the peak-to-average power ratio can result in a substantial improvement in performance and reduction in cost.
Unfortunately, any attempt to reduce the peak-to-average power ratio of a signal by a processing function typically results in reduced spectral performance in the form of splatter, that is, signal energy that extends beyond the frequency band allocated to the signal. Splatter is highly undesirable because it interferes with communications on adjacent channels. Methods used to reduce the peak-to-average power ratio include hard clipping and soft clipping. In hard clipping, each signal magnitude that exceeds a clipping threshold is reduced to a selected maximum value, typically the clipping threshold. Hard clipping results in a high degree of splatter. In soft clipping, the input signal is altered by a non-linear function that reduces the signal peak magnitudes, resulting in less energy being splattered into adjacent channels compared to hard clipping.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions, sizing, and/or relative placement of some of the elements in the figures may be exaggerated relative to other elements to clarify distinctive features of the illustrated embodiments. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of the illustrated embodiments.